In the present state of the art resinoid bonded snagging wheels for conditioning steel billets are comprised primarily of abrasive grain, phenolic resin and fillers.
Generally, the abrasive grains are selected from the group consisting of fused aluminum oxide, fused alumina-zirconia, sintered alumina-zirconia, sintered alumina, sintered bauxite and to a lesser extent silicon carbide.
The phenolic resin portion of the wheel is usually a thermoset mixture of phenolic novolac and hexamethylenetetramine.
The filler portion of the wheel varies from one manufacturer to another, each manufacturer varies fillers to get optimum performance for a particular application. For example, a filler of iron pyrites and potassium fluoborate performs well on stainless steel while a filler of silicon carbide is more efficient on carbon steels.
In formulating abrasive wheel compositions the resin and fillers are usually combined and designated as the "bond" which is mixed with the abrasive particles and other processing ingredients such as wetting agents to provide a hot pressable and a heat post-curable wheel molding composition.
Presently hot pressed steel conditioning snagging wheels contain from 50 to 60 volume percent abrasive with the remainder being "bond" containing at least 42% and often as much as 70% by volume of phenolic resin with the rest being filler.
Up until this discovery it has been considered that wheel durability was largely a function of abrasive content. Loring Coes, Jr., a leading authority on abrasive and grinding wheels stated on page 14 of a book entitled "Abrasives" published in 1971 by Springer Verlag of Wien and New York, "a distinct gain in durability of the wheels can be obtained by using highest possible abrasive content" in organic bonded wheels for severe duty applications.
Contrary to the prior art teachings the herein named inventors have unexpectedly discovered that excellent performance can be obtained from comparable resinoid bonded snagging wheels which have an abrasive content far below current practice by increasing filler content of the wheel and maintaining the resin content of the wheel substantially constant.
U.S. Pat. No. 3,632,320 to Yoshimoni Henmi et al also teaches that grinding efficiency decreases if less than 50% by weight (32% by volume) of abrasive is put into the wheel and the filler content is limited to a maximum of 40% by weight (44% by volume).
Zalud in his U.S. Pat. No. 2,734,813 discloses solving a wheel glazing problem by providing abrasive articles with high filler and relatively low resin content bonds. He teaches utilizing 7-14 parts by weight of thermoset resin binder to 160 parts by weight of abrasive and a filler material comprising 67-95% by weight of the bond which includes the resin binder portion. The essential feature of Zalud invention is to reduce the resin content whereas the instant invention has the object of maintaining a substantially constant volume of resin in wheels with an abrasive content of from 24-45% by volume. Thus, in wheels of the invention the proportion of resin to abrasive actually increases as the abrasive content is decreased.
On the 160 units by weight basis as used by Zalud a standard snagging wheel with 60% by volume of abrasive contains 19.2 units of resin by weight and the invention wheel with 30% volume of abrasive would contain 38.2 units of resin by weight. These figures are well above the 7-14 units taught and claimed by Zalud.
The use of abrasive contents as low as 40% by volume has been taught by Rue et al in U.S. Pat. No. 3,183,071, and Kistler et al in U.S. Pat. Nos. 3, 156,545 and 3,481,723. The example given in U.S. Pat. No. 3,183,071 is based on the displacement molding technique of U.S. Pat. No. 2,860,961 in which the bond is prepared as a hot viscous fluid unsuitable for a standard hot pressing process. In Kistler et al, U.S. Pat. No. 3,156,545 the example wheel consists of 56 volume % abrasive, 21.6% phenolic resin, 7.41% wetting agents and the balance, 15% as filler.
Both Kistler et al and Rue et al disclose incorporating 40% to 64% by volume of abrasive and from 36% to 60% by volume of bond of which Rue et al discloses as containing 43.3% resin and 56.7% of filler and other ingredients including 19.1% furfuraldehyde which may be considered to become part of the resin content. In a 40% by volume of abrasive wheel the bond amounts to 60% by volume which comprises 25.98% resin and the balance of 34.02% includes the other ingredients including fillers and the furfuraldehyde amounting to 11.4% by volume of the wheel. Thus, the 40% abrasive wheel will have (including the furfuraldehyde) a resin content of 37.44% and a reduced filler content (excluding the furfuraldehyde) of 22.56% by volume of the wheel.
Charvat in U.S. Pat. No. 3,864,101 discloses abrasive articles which may contain on a basis % by volume 30 to 50% of 600 to 10 grit size abrasive particles, 26.7 to 53% organic resinous stress absorbing spacer material which includes both cured powder and liquid forms of the resin, about 4% to 24.2% of inorganic filler or spacer material and 0.5% to 25% pores.
The prior art methods of wheel formulation substitutes bond for abrasive to produce softer acting wheels. Since abrasive goes down, the bond including both the filler and resin content goes up. In the invention, the volume of abrasive is much lower and replaced solely by the filler while the resin remains substantially constant with relation to the total wheel.